One example of industrial application of liquid-liquid contacting processes is in liquid-liquid extraction. This entails the mixing of two substantially immiscible liquids of different densities, typically an organic and aqueous solution, wherein a component of interest transfers from one of the liquid phases to the other. Separator vessels are used to contain the liquids and allow separation into their component phases. One process and apparatus for liquid-liquid extraction is described in U.S. Pat. No. 4,338,285 to Eberts issued Jul. 6, 1982 and is incorporated herein by reference.
Since the organic solutions used in such processes generally include flammable solvents of density less than that of the aqueous solution, there is a consequent risk that the upper surface of the organic solution may be ignited within a separator vessel.
Emergency settler drainage systems used heretofore provide for a drainage outlet in the side of each settler at an elevation which includes the interface between the aqueous and organic layers. The emergency outlet is opened automatically in response to fire detectors. The outlet is connected to a drainage conduit which drains the solutions to a suitable containment area. The drainage conduit includes a vertical U-bend to prevent propagation of the fire through the drainage conduit.
Since the elevation of the interface is not fixed, considerable aqueous must be allowed to discharge together with the organic, leading to oversized conduits. Also, since the head of liquid available to discharge the final amount of organic from the settler declines to zero, complete drainage of the organic layer is not to be expected.
Through continuous operation, a gelatinous mixture of aqueous, organic, and solid particles (commonly called crud) often accumulates in the settlers at the organic/ aqueous interface. Conventional apparatus may allow for removal of this gelatinous material by providing a second, normally closed, outlet for organics on each settler, with a set of conduits leading from these outlets to a collection tank. To discharge the material, the aqueous and normal organic outflows are blocked, causing the interface to rise and, by opening the normally closed outlet, allowing the organic layer and gelatinous material to outflow to a collection tank.
The present invention provides means for overcoming the disadvantages of the conventional drainage arrangement and in a manner which utilizes various elements of the apparatus for both emergency drainage and crud removal.